The present invention relates to a coating apparatus for performing coating, mixing, drying, and the like of medical, food, pesticidal products, and the like that are in granular form, and more particularly to a coating apparatus having a rotating drum that is driven to rotate around its axial line.
Coating apparatus having a rotating drum has been used or performing film coating, sugar coating, and the like to medical, food, pesticidal products, and the like that are prepared as tablets, soft capsules, pellets, grains, and in other similar forms (hereinafter collectively referred to as “granules”).
The following Patent Documents 1 to 7, for example, disclose this type of coating apparatus.
Patent Document 1 discloses a coating apparatus having a ventilated rotating drum 30 driven to rotate around a horizontal axial line A, as shown in FIG. 18. The rotating drum 30 is composed of a polygonal tube peripheral wall 30c, one end wall 30a formed in a polygonal pyramid shape extending from one end of the peripheral wall 30c in an axial direction toward one side, and the other end wall 30b formed in a polygonal pyramid shape extending from the other end of the peripheral wall 30c in the axial direction toward the other side. A porous plate 33 is attached to each face of the peripheral wall 30c so that the peripheral wall 30c is ventilated through the porous parts of the porous plates 33. A jacket 34 is attached on the outer periphery of each porous plate 33, and a ventilation channel 35 is formed between the jacket 34 and the porous plate 33.
At the other end of the rotating drum 30 where a rotary drive mechanism including a motor 36 and others is installed, a distributor 37 is disposed for controlling the ventilation of process gas such as dry air for the rotating drum 30. The distributor 37 has the function of communicating the ventilation channels 35 that have come to a preset location as the rotating drum 30 rotates to an air inlet duct 38 and to an air outlet duct 39, respectively.
For example, when one of the ventilation channels 35 comes to an upper part of the rotating drum 30 as it rotates, this ventilation channel 35 communicates to the air inlet duct 38, while, when one of the ventilation channels 35 comes to a lower part of the rotating drum, this ventilation channel 35 communicates to the air outlet duct 39. Thus, the process gas introduced from the air inlet duct 38 into the ventilation channel 35 at the upper part of the rotating drum 30 flows into the rotating drum 30 through the porous plate 33 at the upper part of the peripheral wall 30c, passes through inside a granule layer (rolling bed) 31, flows out into the ventilation channel 35 through the porous plate 33 at the lower part of the peripheral wall 30c, and is exhausted into the air outlet duct 39 through the ventilation channel 35.
Patent Documents 2 to 5 also disclose a coating apparatus having a ventilated rotating drum. Similarly to the apparatus of the Patent Document 1, porous parts are provided in a peripheral wall of the rotating drum for ventilation, and these porous parts are covered by jackets from outside, thereby forming ventilation channels therebetween.
The coating apparatus disclosed by any of Patent Document 6 and 7 has a rotating drum that is not ventilated. The rotating drum shown in the Patent Document 6 or 7 has a circular cross section and a bulged axial center; it is referred to as “an onion pan” because of its shape. Generally, this rotating drum is disposed such that its axial line is inclined to the horizontal. While the rotating drum itself is not ventilated, the ventilation of its inside is achieved through a supply pipe and an exhaust pipe. In the construction shown in FIG. 3 of Patent Document 6, for example, the supply pipe is inserted into the rotating drum from an opening at one end thereof for supplying air, while the exhaust pipe is connected to the opening at one end of the rotating drum for exhausting air. With such ventilation system, however, the process gas such as dry air makes contact only with the surface layer of the granule layer, because of which sufficient ventilation is not achieved to the inside of the granule layer. For this reason, Patent Document 6 shows another construction in FIG. 1 and FIG. 2 in which the air outlet of the exhaust pipe is embedded in the granule layer so as to allow the process gas to pass through inside the granule layer.
Further, as shown in Patent Documents 4 and 5, for example, it is the common practice to provide a baffle (mixing blade) on the inner face of the peripheral wall of the rotating drum in this type of coating apparatus so as to enhance the stirring and mixing effects for the granules to be processed (objects to be processed). The baffle is constructed with a metal plate baffle member formed in a predetermined shape fixed to the inner face of the peripheral wall using a bolt or mounting bracket (see Patent Document 5, for example). The baffle is hollow but its inner space is closed by the peripheral wall (Patent Document 4), or by a lid member (Patent Document 5).    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2001-58125.    [Patent Document 2] Japanese Utility Model Publication No. Sho 43-19511.    [Patent Document 3] Japanese Patent Publication No. Hei 1-41337.    [Patent Document 4] Japanese Patent Laid-Open Publication No. Hei 7-328408.    [Patent Document 5] Japanese Utility Model Laid-Open Publication No. Sho 56-7569.    [Patent Document 6] Japanese Patent Publication No. Sho 55-5491.    [Patent Document 7] Japanese Patent Laid-Open Publication No. Sho 58-40136.
The coating apparatuses shown in Patent Documents 1 to 5 tend to require an elaborate cleaning process after completion of a coating process particularly for the cleaning of the ventilation channels on the inside because of the structure in which the rotating drum is ventilated through the porous parts (or air holes) provided in the peripheral wall, with the ventilation channels being formed between the porous parts and the jackets covering the same from outside.
Moreover, when performing validation on the inside of the ventilation channels after the cleaning, or when wiping off powder or the like of abraded granule particles adhered inside the ventilation channels, the jackets forming the ventilation channels must be removed and then mounted again after the completion of a required procedure, which is troublesome.
Furthermore, when coating granules with sugar liquid or chocolate paste, for example, the rotating drum should preferably be kept at a lower temperature than that of the granules (or objects to be processed) in the case of sugar coating, or at a higher temperature than that of the granules in the case of chocolate coating, in order to prevent these coating materials from adhering on the inner wall of the rotating drum, but the coating apparatuses shown in Patent Documents 1 to 5 cannot be cooled or heated from outside of the rotating drum because the ventilation channels are provided on the outside of the rotating drum. Adhesion of coating material on the inner wall of the rotating drum will cause a complex cleaning or validation process after the coating process, and also lead to a loss of the coating material and a decrease in the product yield.
The coating apparatuses shown in Patent Documents 6 and 7 use a supply pipe and an exhaust pipe for the ventilation of the rotating drum on the inside because the rotating drum itself is not ventilated. The apparatuses thus entail the following problems: If the air vents of the supply pipe and exhaust pipe are located outside the granule layer, the process gas such as dry air cannot provide ventilation for the inside of the granule layer and it takes a long time to dry the granules, or, the granules may be dried unevenly, resulting in deterioration of the coating quality. On the other hand, if the air vent of the supply pipe or exhaust pipe is embedded in the granule layer so as to resolve this problem, powder or the like of abraded granule particles or coating liquid may adhere to the supply pipe or exhaust pipe and clog the air vent, leading to ventilation failure and requiring a complex cleaning process after the coating process, or it may cause contamination. Also, the supply pipe or exhaust pipe embedded inside will inhibit smooth flow of the granule layer and may cause deterioration of the coating quality.
With the coating apparatuses shown in Patent Documents 6 and 7, on the other hand, the rotating drum can be cooled or heated from outside, but if the rotating drum includes a baffle, sufficient cooling or heating of the baffle cannot be expected. Thus there is a problem that coating material such as sugar liquid or chocolate paste tends to stick to the baffle.